1. Field of the Invention
The present invention relates to communication devices and communication methods that exchange data with UWB (ultra wideband) technology.
2. Description of the Related Art
In recent years, UWB (ultra wideband) communication, which is a communication technology that uses an extremely wide frequency band, that can coexist with existing wireless technology and that allows high-speed broadband wireless communication, has garnered considerable attention. UWB communication enables high-speed communication by exclusively using an extremely wide frequency band of several GHz width in the frequency band of 3.1 Hz to 10.6 GHz for short pulses of only about 1 ns duration.
In UWB communication, PPM (pulse position modulation) in which the data is encoded based on the position of the pulse on the time axis is commonly used as the modulation method.
The following is a description of PPM modulation and the circuit configuration of a communication device that is commonly used for PPM modulation. FIG. 6 shows an ordinary communication device for PPM modulation. FIG. 7 is a waveform diagram of a PPM signal. “0101” is taken as an example of input data. In FIG. 6, numeral 600 denotes a communication device, numeral 601 denotes a sender, and numeral 612 denotes a receiver. The communication device 600 includes the sender 601 and the receiver 612. The sender 601 includes a pulse generator 603, an oscillator 602, an antenna 604, and an amplifier 605. The receiver 612 includes a LNA (low noise amplifier) 608, a pulse generator 610, an oscillator 611, and an antenna 607. The pulse generator 603 of the sender 601 generates PPM signals in synchronization with the clock of the oscillator 602. FIG. 7 is a waveform diagram showing the PPM signal generated by the pulse generator 603 of the sender 601. In this example, the pulse is located prior to the timing of the rising edge of the clock waveform when the data is “1”, and the pulse is located after the timing of the rising edge of the clock waveform when the data is “0”. Thus, with the PPM method, whether the data is “1” or “0” depends on the position of the pulses with respect to the clock.
The PPM signal is amplified by the amplifier 605 of the sender 601, and is radiated from the antenna 604. The radiated PPM signal is received by the antenna 607 of the receiver 612. The received PPM signal is passed through the low-noise amplifier 608, and then demodulated.
For the demodulation, the pulse generator 610 generates pulses in synchronization with the clock of the oscillator 611. In a mixer 609, the positions on the time axis of the pulses from the pulse generator 610 and of the pulses of the PPM signal are compared, and a decision whether the data is “0” or “1” is made, thus demodulating the PPM signal and obtaining the output data. The following is a discussion of the pulses serving as the PPM signal. With PPM modulation, a pulse serving as a PPM signal is sent out at every clock signal, and when a “0” follows a “1” or when a “1” follows a “0”, the interval between pulses is narrower than when a “1” follows a “1” or when a “0” follows a “0”. This puts a limitation on the transfer rate. Furthermore, since pulses are generated for each and every data item, there are also problems with regard to energy consumption. Moreover, when the pulse positions in the PPM output change due to problems with regard to jitter and the like, the data cannot be properly received. It should be noted that “jitter” refers to irregularities in pulse amplitude, width, position or the like.